In general, an offshore structure consists of a buoyant platform and a plurality of legs and it has been widely used for offshore operations, such as drilling and completing oil and gas wells in the offshore. At a state in which the movable legs are fully raised up, the buoyant platform is towed to the desired location, the legs are lowered by the jacking system so that the platform is supported on the sea floor. Then the platform is raised above the surface of a body of water for operations. For the purpose of raising or lowering the legs or the platform, a "rack and pinion type" jacking system is widely used. The jacking system of this type includes at least one elongated rack which is mounted vertically on the exterior side surface of the upright legs and extends substantially through the entire length of the same, and a plurality of cooperating pinions engaged with each of the racks. Each of pinions is driven through a series of reduction gears by means of a respective electric motor.
When the platform is supported by the upright legs on the sea floor, this support is effected by the engagement of the rack with the pinion of the jacking system. In this manner, during offshore operations the load which is composed of the self-weight of the platform and environmental forces such as wind, wave, current and others is placed on the jacking system in engagement of the rack with the pinion.
The jacking system generally has large number of pinions in the whole platform. The load on the jacking system is not distributed equally among said pinions for many and various reasons. Therefore, after the platform is jacked up to the desired height, the load on each pinion is commonly adjusted by means of a manual device within certain range.
However as the environmental forces shall increase after the load adjustment, the load on the pinions will become larger unequally owing to the difference of elastic deformation in component of jacking system. In such situation the load on a specific pinion will reach the limit while the load on each of the other pinions will be remained within the limit.